We're planning a significant update for the first half of 2019. It includes a wide range of general improvements and a couple of popular requests. We'll have more to announce on that front next year. With that sorted, we'll move on to additional feature requests.

In the meantime, we do offer a fairly basic search option for the PM inbox, which is, regrettably, fairly easy to overlook. At the bottom of the page, you'll see the phrase "Conversation Options."

From there, you can choose to view messages sent from or received by a particular user. Once you've entered your search criteria, click or tap "set options" on the right side of the screen.

It's not a keyword search, but it can be quite helpful when attempting to track down a particular conversation.